Enabling the Backups are incremental option will run an incremental backup instead of a full one, copying only the changes since your last backup. Currently, the incremental backups are only available for set backups on Unix-like platforms (such as Linux and OS X) and cannot be used when backing up to a remote host.
Additionally, running an incremental backup will update the backup folder in-place so no old backups will be kept if you choose to enable incremental backups.